The present invention relates to a device for the mechanical coupling of two parallel shafts allowing rotatin thereof in a 2/1 ratio (or 1/2 depending on the drive shaft considered).
More precisely, the invention is intended to provide conditions of relative angular rotation with high reliability between two shafts whose rotational axes are parallel but whose rotational movement is limited in a given angular sector less than the limit values .+-..pi./2 for the shaft whose movement is the slowest.
It is desired to attain this aim with high precision and with equipment ensuring a rigid connection, without play, with a minimum of parasite torque and very insensitive to environmental vibrations. One application is in fact contemplated in the avionics field where the airborne optronic equipment is exposed to severe vibrations.
A known technique consists in using the property of the circle according to which the angle at the center is twice the value of the corresponding inscribed angle. This technique uses an assembly derived from that of the crank plate driving a slide beam. The crank plate is reduced to a crank which is integral with a first shaft and which rotates in a defined sector, this first shaft being the one which corresponds to the angle at the center and which therefore rotates the most rapidly. The beam is formed by an arm integral with the second shaft and which has a slide in which moves the crank pin which is at the end of the crank. The distance between the axes of rotation of the parallel shafts is equal to the radius R of the circle and to the length of the crank between the first axis of rotation and the end crank pin. Under these conditions, the second shaft rotates through an angle which is half that of the rotation effected by the first shaft. This solution has the drawback of introducing play between the crank pin and the slide, or friction if this play is reduced or taken up by tighter machining; in addition, the machining of the slide may be considered as fairly delicate for improving the precision.
The aim of the invention is to overcome the drawbacks of this known solution by arranging the assembly so that it offers the technical characteristics mentioned above.